The Haber and Contact processes
The Haber process
- The Haber process makes ammonia:
$$\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$$
- Hydrogen from methane (natural gas); nitrogen from the air.
- Conditions: $450\,{}^{\circ}\text{C}$, about $200$ atm, an iron catalyst.
Practice
The Haber process makes:
N2 + 3H2 ⇌ 2NH3 — ammonia, using an iron catalyst at ~450 °C and ~200 atm.
The Contact process
- The Contact process makes sulfur trioxide (for sulfuric acid):
$$2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$$
- Conditions: $450\,{}^{\circ}\text{C}$, about $2$ atm, a vanadium(V) oxide catalyst.
Practice
The catalyst used in the Contact process is:
The Contact process (2SO2 + O2 ⇌ 2SO3) uses a vanadium(V) oxide catalyst.
Why a compromise
- Pressure: higher gives more product, but very high pressure is dangerous/expensive → a medium pressure.
- Temperature: lower gives more product (forward reaction exothermic), but too slow → a fairly high temperature for a good rate.
- The catalyst speeds it up without moving the equilibrium → lower cost.
Practice
The chosen temperature is a compromise between a good yield and a fast enough rate.
A lower temperature gives more product but is too slow, so a moderately high temperature balances yield and rate.
You've got it
Key idea
- Haber: $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$ — $450\,{}^{\circ}\text{C}$, ~200 atm, iron
- Contact: $2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3$ — $450\,{}^{\circ}\text{C}$, ~2 atm, vanadium(V) oxide
- conditions are a compromise between yield, rate, safety and cost